I did a test uploading a 7mb file with an iphone connection. Using the Xfilesharing script I get an average of 25 kb/sec. I compared it uploading the same file to megaupload and there I get an average of 50 kb/sec. Any Idea why? I had complaints from users and they are preferring to upload to other places using a registered account.

if download/upload get shared (asymetric) then your speed goes down when some1 download

if it is not shared ( full dublex = symetric) then you keep max upload speed/download speed

then it depends on location and server load to
if your server load is high , then upload speed will be slow (as it use a fair amount of cpu to upload)

there are so many things that can prevent big speed uploads , but mainly it is 1 of those

limited connection

distance (high ping)

high cpu load

then the final limitation depends on your host , if you installed/configured your own server or that it was pre configured

in case it is pre configured is it possible that your host limited the connection with a certain script to prevent upload abusing

the best way to test it is by sitting behind your pc , upload the file you like
do the same test with your iphone and compare speeds

depends if you use 3G or wifi if the speed should be the same or a bit lower

for the rest it is hard to debug this kind of stuff if it can be a lot of differend things that limits the speed
but if other users are complaining , try to ask where they are coming from so you can see if it is a certain group or that it is from every where